From 95595c8f60ca995e6ab7e10130265762d504f553 Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Thu, 1 Nov 2018 00:24:48 +0000 Subject: tty: Don't block on IO when ldisc change is pending [ Upstream commit c96cf923a98d1b094df9f0cf97a83e118817e31b ] There might be situations where tty_ldisc_lock() has blocked, but there is already IO on tty and it prevents line discipline changes. It might theoretically turn into dead-lock. Basically, provide more priority to pending tty_ldisc_lock() than to servicing reads/writes over tty. User-visible issue was reported by Mikulas where on pa-risc with Debian 5 reboot took either 80 seconds, 3 minutes or 3:25 after proper locking in tty_reopen(). Cc: Jiri Slaby Reported-by: Mikulas Patocka Signed-off-by: Dmitry Safonov Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- include/linux/tty.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'include/linux/tty.h') diff --git a/include/linux/tty.h b/include/linux/tty.h index fe1b8623a3a1..fe483976b119 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -356,6 +356,7 @@ struct tty_file_private { #define TTY_NO_WRITE_SPLIT 17 /* Preserve write boundaries to driver */ #define TTY_HUPPED 18 /* Post driver->hangup() */ #define TTY_HUPPING 19 /* Hangup in progress */ +#define TTY_LDISC_CHANGING 20 /* Change pending - non-block IO */ #define TTY_LDISC_HALTED 22 /* Line discipline is halted */ /* Values for tty->flow_change */ @@ -373,6 +374,12 @@ static inline void tty_set_flow_change(struct tty_struct *tty, int val) smp_mb(); } +static inline bool tty_io_nonblock(struct tty_struct *tty, struct file *file) +{ + return file->f_flags & O_NONBLOCK || + test_bit(TTY_LDISC_CHANGING, &tty->flags); +} + static inline bool tty_io_error(struct tty_struct *tty) { return test_bit(TTY_IO_ERROR, &tty->flags); -- cgit v1.2.3